Synthetic resin binders, such as phenolformaldehyde, added in the manufacture of fiberboard, such as hardboard and particle board, or used to bond adjacent, e.g. fibrous, material parts such as in the manufacture of plywood, oriented strand board and waferboard, represent a substantial portion of the cost of manufacture. Many attempts have been made to substitute all or a portion of such synthetic resin binders with less expensive components. For example, attempts have been made to utilize lignin-containing spent digestion liquors to form binding resins capable of bonding fibers and fibrous particles in the formation of a fiberboard, as set forth in U.S. Pat. Nos. 2,849,314 and 3,095,392. As set forth in the Guss U.S. Pat. No. 2,849,314, in spite of the many processes proposed for obtaining resinous compositions from sulfite liquor, for the most part such products have found little or no commercial application as thermosetting impregnating agents, binders or adhesives and particularly in the field of production of improved cellulosic and other fibrous materials.
Cellulosic fibers, in the form of comminuted wood, have been treated with caustic for the purpose of making wood pulp for papermaking, rayon, cellophane and the like. However, in each case, the prior art caustic treatment of cellulosic fibers did not result in fiber liquification, since it was desired to preserve the integrity of the cellulose to the greatest degree possible for subsequent use. The following patents teach alkali treatment of cellulosic fibers while maintaining fiber integrity: U.S. Pat. Nos. 1,169,592; 3,871,951; 41,538; 931,606; 2,701,255; 3,013,933; 2,999,783; 2,686,210; 817,960; 1,081,276; 781,733; 774,135; 1,266,957; 3,397,109; 2,541,058; 2,801,264; 2,926,114; 2,697,701; 2,697,702 and 2,697,703.
The Blount U.S. Pat. No. 4,226,982 discloses a method of liquifying cellulose fibers at atmospheric pressure using solid caustic flakes.
In accordance with the Herrick U.S. Pat. No. 3,095,392, a lignosulfonate is added to a reacted mixture of phenol and formaldehyde to form a modified phenol-formaldehyde resin for use as a fluid loss control agent in drilling muds and portland cement slurries.
In accordance with the principles of the present invention, it has been found that new and unexpected results are achieved in the formation of a liquified cellulosic fiber-modified phenol-formaldehyde resin wherein the liquified cellulosic fibers are prepared by heating a mixture of cellulosic fibers in an alkali solution having an alkali concentration of at least 2% by weight at a temperature of at least 140.degree. C. and a pressure of at least 150 psi, wherein the weight ratio of alkali solution to cellulosic fibers is at least 4:1, for a time sufficient to liquify cellulosic fibers.